Control of a passive prosthetic knee joint with adjustable damping

ABSTRACT

Systems and methods for controlling a passive prosthetic knee joint with adjustable damping in the direction of flexion such that a prosthetic unit attached to the knee joint can be adapted for climbing stairs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/768,356, filed Apr. 27, 2010, now U.S. Pat. No. 9,248,031issued Feb. 2, 2016, which is a continuation of U.S. patent applicationSer. No. 12/300,131, filed Nov. 10, 2008, now issued as U.S. Pat. No.7,731,759, which is a national stage application of InternationalApplication PCT/DE2007/000841, filed on May 8, 2007, which claimspriority to German Patent Application No. 10 2006 021802.7, filed on May9, 2006. These disclosures are hereby expressly incorporated in theirentireties by this reference.

TECHNICAL FIELD

The invention relates to the control of a passive prosthetic knee jointwith adjustable damping in the direction of flexion such that aprosthetic unit, with upper attachment elements and with a connectionelement to an artificial foot, which elements are secured on theprosthetic knee joint, can be adapted for climbing stairs.

BACKGROUND

Prosthesis wearers who require a knee prosthesis have to acceptcompromises in terms of the damping of the flexion and extension in theconfiguration of their prosthesis, since passive prosthetic knee jointsare optimized only for certain uses, and, therefore, significantlydifferent movement patterns are either not possible or are only possiblewith extraordinary difficulty. Thus, the movement sequence for walkingon level ground, for which most of the passive prosthetic knee jointswith flexion and extension damping are designed, requires substantiallydifferent damping characteristics than those for climbing stairs.Therefore, with the conventional knee joint prostheses, the prosthesiswearer climbs stairs by a procedure in which, standing in front of thestairs, the healthy leg is lifted onto the first step and thecontralateral leg is then pulled up onto this same step. The walkingspeed may possibly be increased if the healthy leg is placed on everysecond step, but this is very demanding.

In conventional knee joint prostheses designed for walking on levelground, the necessary low extension damping of the prosthetic knee jointhas the effect that, when climbing stairs, an abrupt extension takesplace when pushing oneself upward, and this subjects the prosthesiswearer to an unacceptably high load. Balancing of the leg provided withthe prosthesis is also not possible, because three joints, namely theankle joint, the knee joint and the hip, are arranged one above theother and the prosthesis wearer can only directly control the hip joint.Even when lifting the prosthetic foot in order to reach the next stepup, the problem arises that the prosthetic foot is moved onto the riseror onto the underside of the next step up, since the necessary flexiondamping in the swing phase control for walking on level ground makes itimpossible to reach the top face of the next step up. The flexion drivemechanism provided in active knee joints for the purpose of lifting thefoot and the extension drive mechanism for straightening the knee andlifting the body via the leg provided with the prosthesis is verycomplicated and very heavy. Furthermore, the swing phase control forwalking on level ground is very limited in these active prosthetic kneejoints.

SUMMARY

An object of the present invention is to make available a control modefor a passive knee joint with which an alternating climbing of stairs ispossible for a prosthesis wearer. Advantageous embodiments anddevelopments of the invention are set forth in the dependent claims.

In the control mode according to one embodiment of the invention, apassive prosthetic knee joint with adjustable damping in the directionof flexion allows a prosthetic unit, with an upper element attachable tothe knee joint and a connection element to an artificial foot, to beadapted for climbing stairs. First, a low-torque lift of the prostheticfoot is detected. After the detection of a low-torque lift of theprosthetic foot, flexion damping in the lift phase is lowered,specifically to a level below that which is suitable or optimized forwalking on level ground. By lowering the flexion resistance duringlifting of the prosthetic foot, it is possible to obtain a knee anglethat allows the prosthetic foot to be more easily placed on the nextstep up. More particularly, a flexion of the hip, the low-torque lift ofthe prosthetic foot, and the mass inertia of the prosthetic foot,results in a passive prosthetic knee joint angle which, by bringingforward the hip or by a corresponding extension through the force ofgravity, is sufficient to negotiate the step edge and to position theprosthetic foot over the step. It is advantageous in this case for theweight distribution in the prosthesis to be configured such that thecenter of gravity is arranged as far as possible in the distaldirection, for example in the connection element to the prosthetic footor in the prosthetic foot itself. To this end, for example, the controlunit of the knee system can be arranged distally instead of near theknee such that, without increasing the weight of the prosthesis throughextra weights in the prosthetic foot, the desired effect of the kneeflexion is achieved with a low-torque lift of the prosthetic foot.

During a subsequent foot placement and hip-straightening phase, theflexion damping and optionally the flexion extension is increased toallow the prosthesis to be straightened. In one embodiment, the flexiondamping and possibly the extension damping is increased to a level abovea damping for a swing phase control for walking on level ground, suchthat a controlled extension or straightening of the hip joint, kneejoint and of the ankle joint can take place.

After the step edge has been negotiated, the knee is straightenedthrough the force of gravity. To permit positioning of the prostheticfoot located over the step, the flexion damping is increased prior tostraightening the prosthetic knee joint, such that the prosthetic footcan be positioned via the hip angle directly controlled by the patient.

in the foot placement phase and, if appropriate, the hip-straighteningphase, the flexion damping is preferably increased to a maximum value toreduce or avoid a lowering caused by an insufficient hip-straighteningtorque. In one embodiment, the flexion damping in the foot placement andhip-straightening phase is maintained until the hip is completelystraight.

In one embodiment, extension damping is set during the lift phase, footplacement phase and hip-straightening phase. During the lift phase,extension damping is set to avoid a gravity-induced straightening of theprosthetic knee joint or a dropping of the prosthetic foot. During thefoot placement and hip-straightening phase, extension damping is set toposition the foot down in a controlled manner. In contrast, if extensiondamping was completely absent during the hip-straightening phase, thiswould result in an unnatural upward bounding movement of the patient,which would lead to a stop and an abrupt interruption in maximumextension of the knee joint. In open steps, that is to say withoutrisers, a lifting of the prosthetic foot without extension damping canhave the effect that the prosthetic foot is pushed under the next stepup.

The flexion damping is preferably increased as a function of the changeof the knee angle. As soon as a defined knee angle is reached, which isgenerally greater than a knee angle suitable for walking on level groundin a swing phase control, the flexion damping is increased.Alternatively or in addition, the flexion damping can be increased orlowered as a function of the axial force acting on the lower leg shaft.If the axial force drops sufficiently quickly to approximately zero withthe knee almost straightened, this is an indicator for initiation of astair-climbing mode.

In addition or alternatively to this, the vertical acceleration of theleg, that is to say the thigh or lower leg and hip, can take place witha simultaneous drop in axial force from triggering for activation of acorresponding flexion damping control and extension damping control forclimbing stairs. Moreover, a sufficiently rapid bending of the hip cancause the knee to bend with little or no axial force. Instead of anaxial force, knee-straightening torque, ankle torque or a combination ofthe forces and torques can be detected to initiate the stair-climbingmode.

The detection of a low-torque lift can be achieved mechanically via acaliper or via a force or torque sensor. The caliper can be designed,for example, as a slide which is mounted in a guide and which, withalmost perpendicular lifting of the prosthetic foot, moves into aswitching position that reduces the flexion damping. The measurement ofthe forces or torques can he achieved by known sensor devices.Alternatively, the low-torque lift can take place via a measurement ofthe horizontal acceleration of the prosthetic foot and the detection ofa bending in the knee joint. In contrast to walking on level ground, alow horizontal acceleration of the prosthetic foot, that is to say withalmost perpendicular lifting, causes a high bending to take place in theprosthetic knee joint, which indicates stair-climbing. Moreover, thetorque at the front of the prosthetic foot can he detected to determinewhether the prosthesis user would like to move in a horizontal directionduring walking resulting in a very high loading of the front of theprosthetic foot, or whether there is a reduced axial force and a flexionin the knee joint with the prosthetic foot set down.

To achieve the necessary flexion for negotiating the step height afterthe lift, a flexion support in the lift phase can be achieved via apretensioned spring or another force-storing mechanism Likewise, freeextension can be supported by a spring when a certain time has elapsedafter lowering the flexion damping. This is necessary for safetyreasons, to prevent unwanted damping control in the event of erroneoustriggering of the stair-climbing mode.

The increase of the flexion damping and if appropriate of the extensiondamping is initiated when the prosthetic foot, after being lifted, isplaced down again, for example if an increase of the axial force isdetermined. Alternatively, with the knee angle remaining more or lessconstant, the extension and flexion damping can be increased.

The flexion damping in the lift phase can be lowered to a minimum value,such that the damping effective in each system is not further increasedon account of friction.

The detection both of the low-torque or torque-free lift and also of thelowering of the flexion damping can be done mechanically, and similarlythe changing of the various damping, in order to permit a prosthesisconstruction that is as simple as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment is explained in more detail below withreference to the figures.

FIGS. 1 to 6 are schematic depictions showing the sequence involved inalternating stair-climbing with a passive knee joint prosthesis.

DETAILED DESCRIPTION

FIG. 1 shows a prosthesis wearer 1 with a knee joint prosthesis 2 whichis secured by upper attachment elements to a femoral stump. Theprosthetic leg 20 stands with the healthy contralateral leg 4 in frontof a step.

To reach the next step up, a prosthetic foot 6 has to be guided over thestep edge. An active bending of the hip, as is indicated by the arrow 7,assists the passive bending of the knee, which is shown by the arrow 8and which, because of the mass inertia both of the prosthetic foot 6 andalso of the connection element 3, occurs from the prosthetic knee joint2 to the prosthetic foot 6. For this purpose, a minimum extensiondamping is required to ensure that, after a flexion of the hip, theprosthetic foot 6 does not swing forward and is not moved against theriser or under the step 5. In the lift phase, as shown in FIG. 2, theprosthetic foot 6 is guided upward, as far as possible in aperpendicular manner, this possibly being initiated by a slightrearward. movement. The lift is detected with at least one sensor 10(see FIGS. 1-3) via the flexion angle a between the connection element 3and the thigh or via a reduction of the axial force in the connectionelement 3, without flexion of the prosthetic foot 6. It is also possibleto detect the stair-climbing mode, and thus the lowering of the flexiondamping to a value below the normal swing phase control, preferably tothe minimum value, via a horizontal rearward movement of the prostheticfoot 6 in conjunction with a bending of the hip.

After the step edge has been negotiated and the lift phase completed, asis shown in FIG. 2, a secure positioning of the prosthetic foot 6 on thestep is required, For this purpose, the prosthetic foot 6 has to bemoved forward, which can be achieved by extension as a result of theforce of gravity. For this purpose, an extension damping can be reduced,if this has not already been done in the lift phase. A prosthetic kneejoint 2 that is sufficiently damped in flexion and extension prior tostraightening allows the prosthesis wearer I to position the prostheticfoot 6, by changing the hip angle. In the lowering and hip-straighteningphase, the flexion and extension are preferably strongly damped tocontrol the foot placement, and to prevent a spontaneous backward fallin the event that the hip-straightening torque is insufficient. Theextension remains damped so as to be able to control the speed ofstraightening of the hip and knee. This is shown in FIG. 3.

in FIG. 4, the foot placement phase is completed. The prosthesis wearer1 can initiate straightening of the knee with a hip-straighteningtorque. The straightening of the knee can be assisted by an extension ofthe healthy foot.

FIG. 5 shows the increasing straightening of the knee throughapplication of a hip torque. The increasing straightening of the kneeshortens the effective lever and facilitates the straightening of theknee through the straightening of the hip.

FIG. 6 shows the complete extension of the leg provided with the kneejoint prosthesis 2. The contralateral leg 4 is moved past the prostheticleg 20 and placed on the next step up, such that alternating climbing ofstairs is possible with the passive knee joint prosthesis.

Accordingly, the control is configured in such a way that, during thelift of the prosthetic foot 6 a flexion resistance is set that resultsin a knee angle a, which allows the prosthetic foot 6 to be placed onthe next step. Flexion support by spring mechanisms may facilitate thelifting movement and make it easier to negotiate the step height.

If no action is to take place after the stair-climbing mode has beentriggered by detection of a low-torque lift, a free extension is set,said free extension being set in a time-dependent manner. The timefunction can also be mechanical. The low-torque lift can be detected viathe mass inertia, if the healthy leg is first set down and only thesecond step is intended to be negotiated by the leg provided with theprosthesis. If the prosthetic foot is first unloaded and the prostheticknee joint then bent, the stair-climbing mode is set. Damping both inthe direction of extension and also in the direction of flexion afterthe lift phase, that is to say during the hip-straightening phase, ismaintained until a complete extension of the prosthetic knee joint isreached or detected.

P1. A control of a passive prosthetic knee joint with adjustable dampingin the direction of flexion such that a prosthetic unit, with upperattachment elements and with a connection element to an artificial foot,can be adapted for climbing stairs, said control involving the followingsteps:

-   -   detecting a low-torque lift of the prosthetic food, and    -   lowering the flexion damping in a lift phase to below a level        that is suitable for walking on level ground.

P2. The control in paragraph P1, characterized in that the extensionand/or flexion damping, in a foot placement and hip-straightening phase,is increased to a level above a damping of a swing phase control forwalking on level ground.

P3. The control in paragraph P2, characterized in that the flexiondamping in the foot placement phase is increased to a maximum value.

P4. The control in paragraphs P2 or P3, characterized in that theflexion damping in the foot placement and hip-straightening phase ismaintained until the hip is fully straightened.

P5. The control in one of paragraphs P2 through P4, characterized inthat the flexion damping is increased as a function of the change of theknee angle.

P6. The control in one of the preceding paragraphs (P1-P5),characterized in that the flexion damping is increased or lowered as afunction of the axial force acting on the lower leg shaft.

P7. The control in one of the preceding paragraphs (P1-P6),characterized in that an extension damping is set during the lift phaseand also during the foot placement and hip-straightening phase.

P8. The control in one of the preceding paragraphs (P1-P7),characterized in that the low-torque lift is detected by a force ortorque sensor.

P9. The control in one of the preceding paragraphs (P1-P8),characterized in that the low-torque lift is detected by measuring ahorizontal acceleration of the prosthetic foot and by recording abending in the prosthetic knee joint.

P10. The control in one of the preceding paragraphs (P1-P9),characterized in that a low-torque lift is detected by recording atorque at the front of the prosthetic foot.

P11. The control in one of the preceding paragraphs (P1-P10),characterized in that the flexion in the lift phase is supported via apretensioned spring mechanism.

P12. The control in one of the preceding paragraphs (P1-P11),characterized in that the increase in the flexion and extension dampingis initiated when the prosthetic foot, after being lifted, is placeddown again.

P13. The control in paragraph P12, characterized in that the footplacement is detected by an axial force measurement in the lower legshaft or in the prosthetic foot.

P14. The control in one of the preceding paragraphs (P1-P13),characterized in that the flexion damping in the lift phase is loweredto a minimum value.

P15. The control in one of the preceding paragraphs (P1-P14),characterized in that, after the flexion damping has been lowered, afree extension is set with time control.

P16. The control in paragraph P15, characterized in that the freeextension is spring-assisted.

P17. The control in paragraph P15 or P16, characterized in that the timecontrol is effected mechanically or electronically.

P18. A method for initiating and implementing a stair-climbing mode in apassive prosthetic knee joint connected to a prosthetic leg unitincluding a prosthetic foot comprising:

-   -   detecting a low-torque lift of the prosthetic foot;    -   initiating a lift phase, in which a flexion damping level of the        knee joint is reduced to a. level below that which is used for        walking on level ground;    -   detecting a placement of the prosthetic foot; and    -   initiating a lowering phase, in which the flexion damping level        is increased to a level above that which is used for walking on        level ground.

P19. The method of paragraph P18, wherein in the lowering phase, anextension damping level is increased to a level above that which is usedfor walking on level ground.

P20. The method of paragraph P19, wherein the flexion damping andextension damping are increased to maximum levels in the lift phase.

P21. The method of paragraph P18, wherein the flexion damping is reducedto a minimum level in the lift phase.

P22. The method of paragraph P18 further comprising the step of, duringthe lowering phase, maintaining the flexion damping level until astraightened hip is detected.

P23. The method of paragraph P18, further comprising the step of, duringthe lowering phase, detecting a knee angle and establishing, the flexiondamping level as a function of the detected knee angle.

P24. The method of paragraph P18 wherein at least one of the detectingsteps comprises the step of detecting an axial force along theprosthetic unit.

P25. The method of paragraph P18 wherein an extension damping level isestablished during each of the lifting and lowering phases.

P26. The method of paragraph P18 wherein the step of detecting the lowtorque lift comprises measuring a horizontal acceleration of theprosthetic foot and by detecting a bend in the knee joint.

P27. The method of paragraph P18 wherein the step of detecting the lowtorque lift comprises detecting a torque at the front of the prostheticfoot.

P28. The method of paragraph P18 wherein the step of detecting theplacement of the foot comprises measuring an axial force measurementalong the prosthetic unit.

P29. The method of paragraph P18 wherein after initiating the liftingphase, a time controlled free extension is set.

1-12. (canceled)
 13. A method for controlling a passive prosthetic kneejoint in a prosthetic unit, the prosthetic unit comprising: the passiveprosthetic knee joint; a prosthetic leg unit coupled to the passiveprosthetic knee joint; a prosthetic foot coupled to the prosthetic legunit; at least one sensor; the method for controlling the passiveprosthetic knee joint comprising: detecting with the at least one sensora knee angle of the passive prosthetic knee joint; detecting with the atleast one sensor an axial force in the prosthetic leg unit; initiating astair-climbing mode of the passive prosthetic knee joint when thedetected knee angle indicates a straightened passive prosthetic kneejoint and the detected axial force is approximately zero; activating aflexion resistance control of the passive prosthetic knee joint uponinitiation of the stair-climbing mode.
 14. The method of claim 13,wherein the prosthetic unit comprises an upper element coupled to thepassive prosthetic knee joint, the upper element also being configuredto receive a stump, and wherein the upper element and the passiveprosthetic knee joint form a rigid structure from a location where theknee joint rotates to a location where the upper element is configuredto be coupled to the stump.
 15. The method of claim 13, wherein theflexion resistance control include adjusting a flexion damping of thepassive prosthetic knee joint.
 16. The method of claim 15, whereinadjusting the flexion damping includes lowering the flexion damping to aminimum value.
 17. The method of claim 13, comprising activating anextension resistance control of the passive prosthetic knee joint uponinitiation of the stair-climbing mode.
 18. The method of claim 16,comprising maintaining the minimum value of the flexion damping untildetecting an increase of the axial force.
 19. The method of claim 13,wherein the prosthetic unit comprises a control unit that detects thestair-climbing mode of the prosthetic foot.
 20. The method of claim 13,comprising detecting an acceleration of the prosthetic leg unit, andinitiating the stair-climbing mode of the passive prosthetic knee jointwhen the detected acceleration of the prosthetic leg unit indicates avertical acceleration of the prosthetic leg unit, the detected kneeangle indicates a straightened passive prosthetic knee joint and thedetected axial force is approximately zero.
 21. The method of claim 16,comprising maintaining the minimum value of flexion resistance untildetecting a predetermined minimum knee angle.
 22. The method of claim13, comprising detecting with at least one sensor a foot placement phaseof the prosthetic foot, wherein in the foot placement phase, anextension damping level is increased to an increased level that is abovea level that is used for walking on level ground.
 23. The method ofclaim 16, wherein the flexion resistance control comprises: minimizing aflexion resistance after initiation of the stair-climbing mode;maintaining the minimum resistance until a hip-straightening phase or anextension movement of the knee joint; and increasing the flexionresistance to a maximum value after detecting the hip-straighteningphase or extension movement of the knee joint to avoid a unintendedflexion movement resulting from an insufficient hip straighteningtorque.
 24. A method for controlling a passive prosthetic knee joint ina prosthetic unit, the prosthetic unit comprising: the passiveprosthetic knee joint; a prosthetic leg unit coupled to the passiveprosthetic knee joint; a prosthetic foot coupled to the prosthetic legunit; at least one sensor; the method for controlling the passiveprosthetic knee joint comprising: detecting with the at least one sensoran acceleration of the prosthetic leg unit; detecting with the at leastone sensor a bend in the knee joint; initiating a stair-climbing mode ofthe passive prosthetic knee joint upon detecting the bend in the kneejoint and the detected acceleration of the prosthetic leg unit indicatesa horizontal acceleration of the prosthetic leg unit; activating aflexion resistance control of the passive prosthetic knee joint uponinitiation of the stair-climbing mode.
 25. The method of claim 24,wherein the prosthetic unit comprises an upper element coupled to thepassive prosthetic knee joint, the upper element also being configuredto receive a stump, and wherein the upper element and the passiveprosthetic knee joint form a rigid structure from a location where theknee joint rotates to a location where the upper element is configuredto be coupled to the stump.
 26. The method of claim 24, wherein theflexion resistance control include adjusting a flexion damping of thepassive prosthetic knee joint.
 27. The method of claim 26, whereinadjusting the flexion damping includes lowering the flexion damping to aminimum value.
 28. The method of claim 24, comprising activating anextension resistance control of the passive prosthetic knee joint uponinitiation of the stair-climbing mode.
 29. The method of claim 24,comprising maintaining the minimum value of the flexion damping untildetecting an increase of an axial force in the prosthetic leg unit. 30.The method of claim 24, wherein the prosthetic unit comprises a controlunit that detects the stair-climbing mode of the prosthetic foot. 31.The method of claim 24, comprising detecting a knee angle of the passiveprosthetic knee joint, and initiating the stair-climbing mode of thepassive prosthetic knee joint when the detected acceleration of theprosthetic leg unit indicates a vertical acceleration of the prostheticleg unit, a detected axial force of the prosthetic leg unit is dropping,and the detected knee angle indicates a straightened passive prostheticknee joint.
 32. The method of claim 24, comprising maintaining theminimum value of flexion resistance until detecting a predeterminedminimum knee angle.
 33. A method for controlling a passive prostheticknee joint in a prosthetic unit, the prosthetic unit comprising: thepassive prosthetic knee joint; a prosthetic leg unit coupled to thepassive prosthetic knee joint; a prosthetic foot coupled to theprosthetic leg unit; at least one sensor; the method for controlling thepassive prosthetic knee joint comprising: detecting with the at leastone sensor an acceleration of the prosthetic leg unit; detecting withthe at least one sensor an axial force in the prosthetic leg unit;initiating a stair-climbing mode of the passive prosthetic knee jointwhen the detected acceleration of the prosthetic leg unit indicates avertical acceleration of the prosthetic leg unit and the detected axialforce is dropping; activating a flexion resistance control of thepassive prosthetic knee joint upon initiation of the stair-climbingmode.